In recent years, for compression-encoding of video data, there have been widely used MPEG (Moving Picture Experts Group) or MPEG 2 in which MC (Motion Compensation) processing and redundancy reduction processing by orthogonal transform such as DCT (Discrete Cosine Transform), etc. are combined. Particularly, the video compression encoding technology of MPEG 2and function of the communication satellite have been combined to thereby realize the digital broadcast of image. Further, in future, digital broadcasting of image using ground wave is being realized.
The merit of the digital broadcasting is that a larger number of programs are permitted to undergo transmission in the same transmission path as compared to the analog broadcasting. This results from the fact that image can be compression-encoded.
As a method of carrying out a larger number of programs, the technique called "statistical multiplexing" is proposed. The statistical multiplexing technique is a method of dynamically changing transmission rates of respective programs to decrease transmission rate with respect to, e.g., the program in which degradation of the picture quality is not conspicuous even if the transmission rate is decreased to thereby carry out a larger number of programs.
An example of multiplexing by the fixed rate with respect to three programs, e.g., weather report, news and drama is shown in FIG. 1 for comparison. The abscissa indicates flow of the time, and the ordinate indicates allocation encoding rates with respect to respective programs. In this FIG. 1, respective programs remain to have encoding rate allocated at the initial value and do not change in dependency upon time. The initially allocated values in this case are values allocated (assigned) so that degradation at the portions (times) in which degradation of the picture quality is conspicuous at respective programs can fall within an allowed range. Namely, coding rates more than required are allocated to portions except for those portions.
On the contrary, an example in which four programs are multiplexed by using the technique of statistical multiplexing is shown in FIG. 2. In this case, coding rates of the weather report, news, drama 1 and drama 2 are caused to be dynamically changed. In this case, the point that the fact that portions (times) in which degradations of picture qualities of respective programs are conspicuous overlap with each other at the same time is rare is utilized. For this reason, since when a certain program is the portion in which degradation in the picture quality is conspicuous, degradation in the picture quality of other program is not conspicuous even if coding rate is lowered, coding rates of other program can be allocated to higher degree to the program in which degradation in the picture quality is conspicuous. In this way, programs which are greater than the ordinary case are permitted to undergo transmission.
Meanwhile, conventionally in storing one video program with respect to package media, e.g., Digital Video Disk (DVD) or video CD, an approach is employed in the encoding system for implementing compression-encoding processing to the video information to first measure encoding Difficulty (Difficulty) of picture image of material (data) to carry out, on the basis of its encoding difficulty, bit allocation (distribution) processing every frames of respective video information so as to fall within a given number of bytes within the recording capacity of the package media.
Namely, there was carried out 2 (two) pass encode processing to preliminarily compression-encode non-compressed video data to estimate compression-encoded data quantity thereafter to adjust compression factor on the basis of the estimated data quantity to carry out compression-encoding so that data quantity after undergone compression-encoding becomes equal to a value in conformity with the transmission capacity of the transmission path.
However, when compression-encoding is carried out by this 2 pass encode processing, there is a necessity of implementing, twice, similar compression encoding processing with respect to the same non-compressed video data. Since it is impossible to calculate final compressed video data by one compression-encoding processing, even if attempt is made to compression-encode plural video programs by the statistical multiplexing at the time of digital broadcasting so as to fall within a predetermined transmission rate to carry out transmission thereof, it takes too much time. Namely, it is impossible to compression-encode imaged video data on the real time basis as it is to carry out transmission thereof.
This invention has been made in view of the actual circumstances, and its object is to provide a video data encoding apparatus and a video data encoding method for carrying out, after undergone multiplexing, transmission of plural video programs substantially in real time so as to fall within a predetermined transmission rate.
Moreover, this invention has been made in view of the actual circumstances, and its object is to provide a video data transmission method for carrying out, after undergone multiplexing, transmission of plural video programs substantially in real time so as to fall within a predetermined transmission rate.